Power6 vs Power7 in CPU Performance

I have a number of smallish P6 machines, some of which are coming due for a replacement as part of regular OS and application upgrades.

Does anyone have a gut feel for how the CPU performance of a Power7 core compares to a Power6 core? Most of the time my workload is lots of small tasks where lots of cores are great, but I have a few jobs that are single-threaded and run for 15 or 20 minutes while a human waits. If I replace 4.2 Ghz P6 with 3.7 Ghz P7 am I going to see much gain or loss on these jobs?

If I interpret the rPerf numbers I've seen, I have the feeling I'll see a small improvement. Does anyone have any actual experience that can verify or refute that?

As the Power7 CPU has big dedicated L1 and L2 caches for each core and a
huge shared L3 cache (all internally) you can expect way better performance
when number crunching.

However, the bottleneck may or may not be the I/O performance of such a job.
Latency factors like disks, networks (lan/san) and other resources may have
more impact on the duration of your run than the CPU frequency may
compensate.

The better efficiency of the Power7 may be on par or even better but will
be the same if the latency is not CPU related...

Fact remains, if you want some certainty whether or not to decide for a
faster model like the 6 core 3.7 GHz p740 (8205-E6C3) or 12 core 3.7 GHz
p740 (8205-E6C6) can match or exceed your current performance then just
give your BP or IBM a call.

In several occassions the IBM performance center in Montpellier, France
performed a restore of an mksysb for us on a recommended power server model
and let us perform from remote a couple of benchmark runs on comparable
backend hardware.

Believe it or not but it prooved we needed less cores than ecpected, which
was great 'cause it saved incredible amounts of money on Oracle license and
support-fees eventually, which was invested in more memory and PowerVM
enterprise to allow us more flexibility and performance.
(most databases thrive on RAM over CPU for responsiveness, and the best
database only writes to disk constantly as it can read from memory what it
needs, saving again on index abundance...)

So my advice: prepare some decent benchmark on a testserver for your
specific workload, prepare an mksysb of this, and have a talk with IBM.
As a new contract was signed the time and material for the investigation at
IBM was free!

If your deal is appealing enough for them they might offer you something
similar.
Worse, if your deal is BIG you might even be invited by IBM to come over
onsite :-)

So prepare your case well and you may be up for a couple of surpises ;-)

As the Power7 CPU has big dedicated L1 and L2 caches for each core and a
huge shared L3 cache (all internally) you can expect way better performance
when number crunching.

However, the bottleneck may or may not be the I/O performance of such a job.
Latency factors like disks, networks (lan/san) and other resources may have
more impact on the duration of your run than the CPU frequency may
compensate.

The better efficiency of the Power7 may be on par or even better but will
be the same if the latency is not CPU related...

Fact remains, if you want some certainty whether or not to decide for a
faster model like the 6 core 3.7 GHz p740 (8205-E6C3) or 12 core 3.7 GHz
p740 (8205-E6C6) can match or exceed your current performance then just
give your BP or IBM a call.

In several occassions the IBM performance center in Montpellier, France
performed a restore of an mksysb for us on a recommended power server model
and let us perform from remote a couple of benchmark runs on comparable
backend hardware.

Believe it or not but it prooved we needed less cores than ecpected, which
was great 'cause it saved incredible amounts of money on Oracle license and
support-fees eventually, which was invested in more memory and PowerVM
enterprise to allow us more flexibility and performance.
(most databases thrive on RAM over CPU for responsiveness, and the best
database only writes to disk constantly as it can read from memory what it
needs, saving again on index abundance...)

So my advice: prepare some decent benchmark on a testserver for your
specific workload, prepare an mksysb of this, and have a talk with IBM.
As a new contract was signed the time and material for the investigation at
IBM was free!

If your deal is appealing enough for them they might offer you something
similar.
Worse, if your deal is BIG you might even be invited by IBM to come over
onsite :-)

So prepare your case well and you may be up for a couple of surpises ;-)

If your smallish jobs have small cache requirements then Migrating to p7 is
good option
It is not always a good idea to replace multiple small machines with
Midsized virtualised server
Running p6 with with 30% more cores is more economical than Replacement
with PowerVM
As far as performance is concerned there are more areas to be understood in
I/O environment

For Physical capacity look at lparstat or vmstat command ( entc ) what
lsdev reports is the virtual processors which are whole numbers. Logical
processor is a result simultaneous multi threading (SMT).